1. Field of the Invention
The present invention relates to an alignment method and an alignment apparatus for aligning, when an evaporation material is evaporated via a mask onto a substrate, the substrate and the mask with each other, and further, to an organic electroluminescent (EL) element manufacturing apparatus including the alignment apparatus.
2. Description of the Related Art
Generally, in an organic EL element, a hole transport layer, a light emitting layer, on electron transport layer, and the like, are formed as organic thin film layers between an anode formed of a transparent conductive film (for example, indium tin oxide (ITO)) and a cathode formed of a metal (for example, Al). An organic EL element is an electronic device that attains light emission by causing a hole injected from the anode side and an electron injected from the cathode side to recombine with each other in the light emitting layer via the hole transport layer and the electron transport layer, respectively.
In a manufacturing process of the organic EL element, a so-called mask evaporation method is known in which a mask is used to evaporate a specific material onto a substrate. By using the mask evaporation method, a red, green, or blue organic EL light emitting layer may be formed even in a very small region on the substrate. In the mask evaporation method, it is necessary to carry out an alignment operation between the substrate and the mask, and to evaporate an organic EL material at a predetermined position. Generally, the alignment operation is carried out by taking, with a camera, images of alignment marks provided en the substrate and the mask, respectively, processing the images, recognizing the positions thereof, and mechanically aligning the positions of the marks. Ordinarily, the alignment operation is carried out after the substrate is brought into an evaporation apparatus. A relative positional error between the alignment marks is determined immediately after the substrate is brought in when the substrate and the mask are away from each other, and when the substrate is brought into contact with the mask. In determining an error between the alignment marks after the substrate is brought into contact with the mask, when the error is outside a target error range, the substrate is once detached from the mask, and the alignment operation is carried out again.
In an organic EL element manufacturing apparatus using such an alignment method, as disclosed in Japanese Patent Application Laid-Open No. 2008-4358, there is known a method of improving the alignment accuracy based on the difference in calculated amount of movement during the alignment operation in an alignment step.
However, as described above, it is often the case that the alignment operation between substrate and the mask is carried out immediately after the substrate is brought in, and the positions of the alignment marks on the substrate and the mask are recognized using a camera with the substrate vibrating in the direction of gravity. When the substrate is vibrating in the direction of gravity, the alignment marks are seen as if the size thereof changes, which affects the recognition rate and the positional accuracy of the alignment marks after the image processing. The lowered recognition rate of the alignment marks may cause the error to be outside the target error range, and may cause the substrate and the mask to be repeatedly brought into contact with each other, which may result in damage of the substrate and the mask, an inconsistent processing time, and difficulty in improving the productivity.